In recent years, in radio communication, particularly in mobile communication, various kinds of information such as images and data other than speech have become targets of transmission. Demand for higher-speed transmission is likely to increase in the future, and, to realize high-speed transmission, a radio transmission technique is desired that realizes high transmission efficiency by utilizing limited frequency resources efficiently.
Radio transmission techniques that respond to this demand include OFDM (Orthogonal Frequency Division Multiplexing). OFDM refers to a multicarrier transmission technique for transmitting data in parallel using a large number of subcarriers, and is known as a technique that has high frequency efficiency and characteristics of reducing inter-symbol interference under a multipath environment and that is effective in improving transmission efficiency.
Performing frequency scheduling transmission and frequency diversity transmission when this OFDM is used in downlink and data for a plurality of radio communication mobile station apparatuses (hereinafter simply “mobile stations”) is frequency-domain-multiplexed on a plurality of subcarriers, is studied (for example, see Non-Patent Document 1).
With frequency scheduling transmission, a radio communication base station apparatus (hereinafter simply “base station”) allocates subcarriers to mobile stations adaptively based on received quality of each frequency band at the mobile stations, so that it is possible to obtain a maximal multi-user diversity effect and perform communication very efficiently. Such frequency scheduling transmission is a scheme suitable for data transmission mainly when the mobile station moves at low speed. On the other hand, frequency scheduling transmission requires feedback of received quality information from the mobile stations and so is not suitable for data transmission when the mobile station moves at high speed. Further, frequency scheduling is generally performed per subband which is obtained by dividing adjacent subcarriers into blocks, and so cannot provide a very high frequency diversity effect.
In Non-Patent Document 1, a channel for performing this frequency scheduling transmission is referred to as a localized channel (hereinafter “Lch”). Conventionally, Lchs are allocated in subband units or in units of a plurality of consecutive subcarriers. Further, generally, adaptive control such as adaptive modulation is performed on Lchs per subband (in the frequency domain) and per subframe (in the time domain). For example, to achieve a required error rate, the base station performs adaptive control on an MCS (Modulation and Coding Scheme) of Lch data symbols based on received quality information fed back from the mobile station.
In addition, Non-Patent Document 1 discloses an example where one frame (10 ms) is divided into 20 subframes (one subframe=0.5 ms) and one subframe includes six or seven OFDM symbols.
By contrast with this, frequency diversity transmission allocates data for the mobile stations to subcarriers in the full band in a distributed manner, and so can provide a high frequency diversity effect. Further, frequency diversity transmission does not require received quality information from the mobile stations, and so is an effective scheme in a state to which frequency scheduling transmission is difficult to apply as described above. On the other hand, frequency diversity transmission is performed regardless of the received quality at the mobile stations, and so cannot provide a multi-user diversity effect as in frequency scheduling transmission. In Non-Patent Document 1, a channel for performing such frequency diversity transmission is referred to as a distributed channel (hereinafter “Dch”). Conventionally, Dchs are set according to FH (Frequency Hopping) patterns which cover the whole band of OFDM symbols.    Non-Patent Document 1: R1-050604 “Downlink Channelization and Multiplexing for EUTRA” 3GPP TSG RAN WG1 Ad Hoc on LTE, Sophia Antipolis, France, 20-21 Jun., 2005